Railroads are generally constructed on a base layer of compacted, crushed stone material. A layer of gravel ballast rests on top of this stone layer. Crossties are laid in and on this ballast layer, and two parallel steel rails are attached to the crossties with fasteners. The majority of crossties in service are made of wood. Various other materials are used such as concrete, steel, and composite or recycled material in the manufacture of crossties.
The ties are normally paced on top of the track ballast. The remaining construction differs slightly depending on the type of tie material useds. If wood ties are used, tie plates are then placed on top of the ties. Rails are then placed on top of the tie plates. The rails are then fastened to the ties through the use of spikes or bilts driven through holes in the tie plates. When concrete ties are used, rails are placed on top of the ties, with a thin polymer pad preventing direct contact between the steel and the concrete. Steel clips are often used to fasten the rail to the tie. Additional track ballast is then used to fill spaces between and around the ties to assist in anchoring.
Normal railroad traffic causes friction between ties and rails, as well as rails and spikes, bolts, screws, or clips, and the surface under the ties. Of particular concern is friction at the point where the rail seats against the tie. Wear at this point, also known as rail seat abrasion, directly impacts the life of the tie by causing it to loosen from the rail. In spite of the pads used between rails and concrete ties, rail seat abrasion remains a continuing problem with concrete ties.
When the rail seat wears, it affects the amount of tension on the fastener so that the rail mounting force required to firmly affix it to the tie is not achieved. Should this happen, the rail can slide against the tie, which increases the rate of abrasion. Rail slide can also cause rail welds to pull apart, either from stress or from temperature misalignments. Another concern with rail seat abrasion is that it increases the exposure of the surface of the ties to environmental conditions, further accelerating rail seat abrasion and tie degradation. Additional causes or contributing factors to rail seat abrasion can include manufacturing defects, temperature variation patterns, railroad arrangements, such as curvature, grade, and banking, and the state of the pad used between rail and tie.
Measurement has been conducted to monitor the wear of concrete ties, either by direct manual measurement, or through the use of electronic devices installed below individual railroad ties. All previous methods have proved either unreliable, hazardous, labor-intensive, requiring extensive equipment installation, or having a major impact on the availability of railroads to train traffic.
In view of the foregoing, the present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above, thereby providing a system capable of predicting instances of rail track abrasion without the need for hazardous and unreliable manual measurements or costly electronic measurement devices.